The present invention relates to a high-performance integrated microactuator. In particular, the integrated microactuator according to the present invention is advantageously but not exclusively used for actuation of hard disk read/write transducers, to which the discussion below will make explicit reference without thereby losing generality.
Integrated microactuators have recently been proposed in hard disk actuating devices provided with a dual actuation stage, wherein a first actuation stage performs a coarse drive of a read/write (R/W) transducer during tracking and a second actuation stage performs a finer position control of the R/W transducer.
An example of a hard disk actuating device 1 with a dual actuation stage is shown diagrammatically in FIGS. 1 and 2. In detail, in FIG. 1, the hard disk actuating device 1 comprises a motor 2 (also called a xe2x80x9cvoice coil motorxe2x80x9d) to which at least one suspension 5 formed by a lamina is fixed in a projecting manner. At its free end, the suspension 5 has an RW transducer 6 (see, e.g., FIG. 2), also known as a xe2x80x9csliderxe2x80x9d and disposed (when in an operating condition) facing a surface of a hard disk 7 (see, e.g., FIG. 1). The R/W transducer 6 is fixed to a coupling, known as a gimbal 8, via a microactuator 9 interposed between the gimbal 8 and the R/W transducer 6 (see, e.g., FIG. 2). On one of its lateral surfaces, the R/W transducer 6, formed by a body of ceramic material (such as AlTiC), further has a read/write head 10 (magneto/resistive and inductive) which forms the actual read/write device.
In the actuating device 1, the first actuation stage is defined by motor 2 that moves the unit formed by suspension 5 and R/W transducer 6 across the hard disk 7 during track seeking, and the second actuation stage comprises the microactuator 9 that finely controls the position of the R/W transducer 6 during tracking.
An embodiment of a microactuator 9 of a rotary electrostatic type is shown schematically in FIG. 3, wherein microactuator 9 is shown only in part, given its axial symmetry. The microactuator 9 comprises an external stator 17, integral with a die embedding the microactuator 9 and bonded to the gimbal 8, and an internal rotor 11, intended to be bonded to the R/W transducer 6 (see, e.g., FIG. 2) and capacitively coupled to the stator 17.
The rotor 11 comprises a suspended mass 12 of substantially circular shape and a plurality of movable arms 13 extending radially towards the outside from the suspended mass 12. Each movable arm 13 has a plurality of movable electrodes 14 extending in substantially circumferential direction and equidistant from each other. The rotor 11 further comprises anchoring and elastic suspension elements (shown as springs 15) elastically connecting the suspended mass 12 to fixed anchoring regions 16 that bias the rotor 11 and the movable electrodes 14 at a reference potential.
The stator 17 comprises a plurality of fixed arms 18a, 18b extending radially with respect to the suspended mass 12 from fixed biasing regions 20a, 20b arranged circumferentially around the rotor 11 and each fixed arm 18a, 18b having a plurality of fixed electrodes 19. In particular, a pair of fixed arms formed by a fixed arm 18a and a fixed arm 18b is associated with each movable arm 13. The fixed electrodes 19 of each pair of fixed arms 18a, 18b extend towards the associated movable arm 13 and are intercalated or interleaved with the movable electrodes 14. All the fixed arms 18a are disposed on a same side of the respective movable arms 13 (e.g., on the right side in the example shown in FIG. 3) and are all biased at a same first drive potential through bias regions 20a. Similarly all the fixed arms 18b are arranged on the other side of the respective movable arms 13 (e.g., on the left side in the example shown in FIG. 3) and are all biased at a same second drive potential through the bias regions 20b. 
The fixed arms 18a and the fixed arms 18b are biased at different drive potentials which differ from the reference potential of rotor 11 so as to generate two different potential differences with respect to the movable arms 13 and to cause the rotor 11 to rotate in one direction or the other.
Materials currently used to manufacture the microactuator 9 are substantially of two types: brittle materials, such as single or multi-crystal silicon, which are elastically but not plastically deformable, and ductile materials such as nickel that are plastically deformable.
Specific assessments of the energy dissipation capacity of these materials, the obtainable reliability, and the effects of their use on the final quality control process of the finished product cause silicon to be chosen as the structural material. In fact, the use of silicon enables microstructures to be produced which are more reliable than if metals are used, with considerable simplifications to the final quality control process of the finished product.
On the other hand, silicon microactuators have a damping factor that is much worse than metals. In fact, a microactuator of silicon may be modelled by means of a second order differential equation defined, inter alia, by a damping factor, or alternatively, by a quality factor inversely proportional to the damping factor, both of which contribute to defining a response of the microactuator to an application of a step stress.
In particular, a microactuator of silicon typically has a quality factor which is too high (comprised, e.g., between 10 and 1000) for the considered applications (e.g., with too low a damping factor comprised, e.g., between 5. 10xe2x88x924 and 5. 10xe2x88x922), and thus has a step response having over-elongations of a very high amplitude compared with a stationary value.
Consequently, during fine position control of the R/W transducer 6 that determines accurate positioning of the R/W transducer 6 at a read position, microactuators of silicon have the disadvantage of having rather high settling oscillations (e.g., xe2x80x9cringingxe2x80x9d) about the read position, such as to require the use of very complex closed-loop control circuits for damping such settling oscillations and thus to enable acceptable settling times of the R/W transducer 6.
An advantage of an embodiment of the present invention is to provide an integrated microactuator to address disadvantages of known integrated microactuators.
An embodiment of the present invention provides an integrated microactuator comprising a stator element and a rotor element capacitively coupled. The rotor element comprises a suspended mass and a plurality of movable drive arms extending from the suspended mass and biased at a reference potential. The stator element comprises a plurality of first fixed drive arms facing respective movable drive arms and biased at a first drive potential. A mechanical damping structure for settling oscillations of the rotor element is interposed between at least a part of the stator element and a part of the rotor element.